Method and means for selecting character inclination in cathode ray tube displays



Jan. 7, 1969 c. E. MURDocK ETAL 3,421,044 METHOD AND MEANS FOR SELEGTING CHARACTER INCLINATION IN CATHODE RAY TUBE DISPLAYS Filed April 2l, 1967 Sheet INVENTORS Jan. 7, 1969 [gcTloN-I @NVEQGENCEI L' loo UNBLANK l AND Ol CHARACTER BIAS REFERENCE E. MUR'DCDCF` ET AL METHOD AND MEANS F Filed April 2]... 1967 OR SELECTING CHARACTER INCLINATION IN CATHODE RAY TUBE DISPLAYS Shee'fl 2 of 2 INVENT ORS CLAYTON EMURDOCK DONALD J. PUGH ROBERT H COMPTON GEM ATTORNEYS United States Patent Oftice 3,421,044 Patented Jan. 7, 1969 3,421,044 METHOD AND MEANS FOR SELECTING CHAR- ACTER INCLINATION IN CATHODE RAY TUBE DISPLAYS Clayton E. Murdock, Donald J. Pugh, and Robert H.

Compton, San Diego, Calif., assignors to Stromberg- Carlson Corporation, Rochester, N.Y., a corporation of Delaware Filed Apr. 21, 1967, Ser. No. 632,815 U.S. Cl. 315-14 15 Claims Int. Cl. Htlli 29/ 56 ABSTRACT OF THE DISCLOSURE This disclosure provides for control of displays produced by cathode ray tubes such as electron beams formed into shape or deection patterns of different alphabetic symbols and generating a display in some such visible form as a presentation on a phosphor screen. Control of the rotation of the beam thus shaped takes place as it passes through the tube so that the inclination of the characters on the display may be chosen at will to form for example vertical and horizontal lines. In particular, a plus/minus 45 degree ybeam rotation of the nominal beam orientation takes place to provide a 90 degree inclination shift of produced characters without change in the beam focus when the beam is rotated by an electromagnetic coil. This change of inclination of characters is described in connection with diiferent cathode ray tube embodiments having magnetic and electrostatic convergence means, character size controls and multiple function electromagnetic coils serving to converge, focus, and rotate the beam.

This invention relates to development of printed text by electronic methods and, more particularly, it relates to formation of character displays upon the screen of a cathode ray beam tube.

The art of producing character displays upon the screen of a cathode ray tube by deflection of the beam through selected positions on a pattern mask which shape the beam is well known and highly developed. However, a single axis of orientation of the character displayed has been generally established by the pattern in the mask. For graphic art purposes of making graphs or other display forms it is often desirable to have characters either vertically or horizontally oriented at will on various parts of a total display. If this is accomplished by characters of various orientations in the mask, the character selection and beam forming process becomes complicated and less reliable.

It is therefore a general object of this invention to provide electronically controllable means for changing the orientation of a displayed character on a cathode ray tube screen at will.

A further object of the invention is to provide an eicient and effective electronic system of character orientation which presents characters produced in a single orientation at a pattern mask of a cathode Iray tube in either horizontal or vertical inclinaion upon the screen of the cathode ray tube.

Thus, in accordance with a preferred embodiment of the invention a focus coil is used to rotate the shaped beam alternately through two equal but opposite angles such as plus/minus 45 from the orientation of the characters in the pattern mask to produce lrespectively the desired horizontal and vertical inclination of characters on the screen. This is effected selectively by means of transistorized electronic circuitry 4with a suitable electronic control signal waveform.

The invention is described in greater detail in the following specitication by means of a specific embodiment as referenced to the accompanying drawings, wherein:

FIGURE 1 is a diagrammatic view partly in perspective of structure in a cathode ray tube illustrating general operational principles of the invention;

FIGURE 2 is a schematic diagram of an electronic switching circuit for selectively changing the inclination of displayed characters in accordance with this invention;

FIGURE 3 is a diagrammatic view in section of a practical cathode ray tube embodiment of the invention utilizing elecrostatic convergence;

FIGURE i4 is a further cathode ray tube embodiment in diagrammatic section view providing for variable character size;

FIGURE 5 is a further cathode ray tube embodiment in section view which employs magnetic convergence; and

FIGURE 6 is a cathode ray tube circuit configuration with the tube in section and including block circuit diagrams operable in the present invention to produce both convergence and rotation of the electron beam by the same coil.

It may be seen from FIGURE 1 that a beam formed in electron gun 5 passes nominally along the beam axis 6 within the cathode ray tube contained in envelope 7 until it strikes a phosphor screen 8 upon `which a visual display is developed. The 4beam itself is shaped into such form by mask 9 that it forms legible characters or symbols 10 when it strikes the screen 8. To select the desired character, line or symbol the beam is deected by conventional character selection controls 11 to an appropriate aperture 12 in mask 9. It is obvious, however, that this invention also applies to other means of forming a shaped beam such as by control of emission paterns or by control of deflection circuits to scan the beam over a pattern area.

Since the shaped beam path after passing mask 9 is generally in a deflected position, a focus and convergence coil 15 is supplied which returns the beam back to the avis 6 when placed in the proper position along the beam and also serves to focus the shaped beam. Thus, a larger character 16 near the mask 9 is reduced in size 17 after passing the focus coil 15. This focus-convergence coil 15 also serves to rotate or incline the character as it passes through the coil as seen from comparison of beam patterns 16 and 17. ln accordance with this invention proper control of this rotation is effected in the focus control circuit 29 to selectively direct the inclination of characters on the cathode ray tube screen 8, so that for example, they :may be presented either in vertical (21) or horizontal (22) inclination. The display position of the characters on the face of the tube is conventionally established by means of deflection coils 23 along with deflection control circuits Z4.

Therefore, in accordance with this invention it has been found that the rotation of the beam in focus coil 15 is reversible with a change in direction of current tlow through the coil. Thus, assuming a 45 incident orientation of characters 30, as shown in FIGURE 2, which would prevail should no current flow through the `focus coil 15, the direction of the rotation can be changed to either vertical or horizontal by selectively controlling current ilow only enough to produce a plus or minus 45 rotation from nominal annotated beam orientation. This can be accomplished by means of a simple electronic control waveform signal Es at the input terminal 35 of the electric current embodiment shown.

In essence, the electronic circuit is a two channel switch controlled by the input signal Es to activate one or the other of the focus coil current control transistors 36, 37, to thereby establish current flow in one of two opposite directions established from the respective plus or minus 2O volt supply source terminals. Thus, a corresponding change of beam rotation from 21 to 22 'or vice versa follows a change of level in the input control signal waveform Es.

One of the input switching transistors 40, 41 is made conductive by the input signal Waveform level to establish at transistor 42 a control signal of amplitude established by the respective potentiometer 43 or 44. The power source levels are stabilized -by means of Zener diodes 45, 46 at this low level circuit position. Transistors 42, 66, 48, 53, 54, 36, and 37 and the associated resistors comprise a high gain, high power amplifier. The input stage 50 of the amplifier is a differential amplifier using transistors 42, 66 coupled by common emitter resistor 69 and providing an output signal at load resistor 51. Transistor 48 is an inverting voltage amplifier. Transistors 53 and 54 are medium power emitter followers which drive the power output stage 52. Power transistors 36 and 37 together are a complementary emitter follower power amplifier output stage. Negative feedback is applied to one of the differential input terminals through resistor network 65, 67 to stabilize the output current flowing in the load, coil 15. Differential amplifier stage f) has transistors 42, 66 which respond to any differences (or error) in the signal voltages impressed on the base electrodes of transistors 42, 66. Any difference in the base potentials is amplified and appears at the collector elecrode resistor 51 of transistor 42, and is supplied to the base 'of transistor 48. Transistor 48 further amplifies the error signal which is then passed through the driver stage 47 including transistors 53, 54 to the power emitter follower output stage including transistors 36, 37. Current is supplied to the rotation control coil by the power stage transistors 36, 37. Coil current is sampled by resistor 65, which produces a voltage proportional to coil current. The sample voltage is supplied via resistor 67 to the base electrode of transistor 66 as feedback voltage to close the loop of the feedback control amplifier.

The reference voltage to the differential amplifier 50 is supplied by the input stage 55. Thus, when the input signal Er is positive with respect to ground at terminal 35, transistor 40 conducts, clamping its collector and the output of potentiometer 43 to ground. Transistor 41 is cut off by the positive voltage of Es and its collector draws no current, hence half of the voltage from the slider of potentiometer 44 is supplied to the base electrode of transistor 42. The base of transistor 42 is then at approximately 2.5 volts. If the current in the coil 15 is then -1 ampere (1 ampere through transistor 37 to -20 v. supply), the feedback sample voltage across resistor 65 will be 2.5 v., approximately the same as the input signal supplied to the base of transistor 42.

If the current in coil 15 were less than one ampere, the base of transistor 66 would be more positive than the base of transistor 42. The difference would be amplified and appear as a larger positive error signal at the base of transistor 48. Transistor 48 would amplify and invert this error signal and apply a larger negative error signal to the drivers 53, 54. The driver 54 would respond by conducting more heavily, which would make power transistor 37 conduct more heavily. The current in coil 15 and sample resistor 65 would thus increase in magnitude until the feedback voltage became closely equal to the input voltage to transistor 42. If the current in coil 15 and sample resistor 65 were greater than 1 ampere, the -base of transistor 66 would be more negative than the base of transistor 42, and the error signal amplified by transistor 48 would be of positive polarity, and would cause power amplifier transistor 37 to conduct less heavily. In the case of positive Es, driver 53 and power transistor 36 are nonconducting. The circuit of FIGURE 2 thus regulates the current in coil 15 to a constant value determined by potentiometer 44 when the input signal Es is positive.

When the input signal Es is negative with respect to ground, transistor 40 is cut off and transistor 41 shorts the output of potentiometer 44 to ground. Half of the voltage on the slider of potentiometer 43 is then applied as an input signal to the feedback control amplifier. The base of transistor 42 is then at approximately plus 2.5 v. The feedback amplifier regulates the current in coil 15 to about +1 ampere (l ampere through transistor 36 to the +20 v. supply). Driver transistor 54 and power transistor 37 are cut off in this case (Es negative). The circuit of FIG- URE 2 thus regulates the current through coil 15 in a similar manner as heretofore explained to a constant value determined by the setting of potentiometer 43, when Es is negative.

Since the coil is inductive, diodes 60, 61 are provided to discharge any high voltage inductive transient as the abrupt switching takes place, changing the direction of current flow through coil 15, thereby protecting the power transistors 36, 37.

While the cathode ray view of FIGURE 1 serves to illustrate the general principles and objectives of the invention, the actual -beam formation and rotation may be accomplished practically in several different ways as exemplified in the following representative constructions of FIGURES 3-6.

Thus, in FIGURE 3 showing a cathode ray tube with electrostatic convergence means; the beam of electrons formed in electron gun 5 passes along a path 14 until it strikes the phosphor screen 8. The beam is shaped by mask 9 into such form that it produces legible characters on the screen. To select the desired character, from a multiplicity of characters on mask 9, the beam is defiected off axis 6 by electrostatic deflection plates 80, 81, 82 so that it strikes an appropriate aperture in mask 9.

Since the shaped electron beam, after passing mask 9, is generally in a defiected position, an electrostatic convergence lens array 83, 84, 85 is supplied which bends the beam back toward the axis. The direction of the beam as it exists the lens element 85 is such that it would intersect the axis 6 near the center of electrostatic plates 87. Between plates 87 the beam is generally on the axis but not traveling parallel to the axis. Electrostatic reference plates 86, 8-7, 88 are provided to again bend the beam, so that travel parallel to (and on) the axis is achieved. The elements of FIGURE 3 described so far are not novel but are well known in the art of shaped beam tubes.

In this invention an electromagnet with an outer ferromagnetic shell and inner coil 89 provides substantially axial fiux to produce rotation of the shaped beam about its own center. It has been found that an electromagnet produces such rotation, wherein the electrons at the center of the cross section of the beam are not affected by the axial magnetic field of the coil, but all other electrons are forced into spiralling trajectories, so that the cross section of the shaped beam is rotated. When it is desired that characters on the screen have two selectable orientations, differing by degrees, the current in the rotation coil is adjusted to produce a rotation of 45 degrees. Reversal of the current then produces rotation of 45 degrees in the opposite direction, or a change in orientation of 9() degrees at the screen. The display position on the face of the tube is conventionally established by deflection coils 23.

In prior art, without the rotation coil 89, the strength of the convergence lens array 83, 84, 85 and its position relative to the other tube elements, were adjusted so that it simultaneously formed a focused electron image of the mask 9 on the phosphor screen 8, and produced axis crossover in reference plates 87 of beams deflected from the axis by selection plates 81. Thus Ialso insured axis crossover in the center of the set of plates 86, 88 of a beam defiected by the set of plates 80, 82, since the sets 80, 81, 82 and 86, 87, 88 are coplanar sets as described in U.S. Patent 2,811,668. In this invention the rotation coil 89 as well as the electrostatic convergence lens have focusing effects in addition to their rotation and convergence effects. The combination of two focusing effects produces an electron image of mask 9 on the screen 8. Reversal of the current in coil 89 does not change its focusing effect, hence both images (at plus 45 degrees and -45 degrees) may be in sharp focus. If the current coil 89 were switched from zero to a value producing 90 degrees rotation, one or the other of the two characters would be out of focus. The use of plus/minus 45 degrees rotation is therefore 4advantageous when a 90 degree change in orientation is desired.

It will be obvious to those skilled in the art that the embodiment of FIGURE 3 would also operate if the coplanar selection and reference plates were replaced by conventional electrostatic plates, or by coplanar electrostatic deectors of the circumferentially interleaved type, known as Deflectrons Some degradation of quality and precision of operation may result from the use of conventional plates, however. It is also obvious that electrostatic convergence lenses having more or fewer electrodes than FIGURE 3 may be used, and rotation coils may successfully be made either with or without pole pieces, housings, or shields of magnetic material. Furthermore, the rotation coil may be short in axial length with a small air gap, as in a conventional focus coil, or long in axial length, as in a magnetic convergence coil or Vidicon focus coil.

In the embodiment of FIGURE 4, provision is made to change the character size and thus, this is a preferred embodiment. The electron gun 5, coplanar selection places 80, 81, 82, mask 9, electrostatic convergence lens array 83, 84, 8S, and coplanar reference plates 86, 87, 88 operate identically to the corresponding elements of FIG- URE 3.

An electrostatic lens 90, 91, 92 is added between the reference plates 86, 87, 88 and the rotation coil 89, to enable variation of the size of the characters displayed on the phosphor screen. In practice, the voltage lapplied to two elements of the size control lens array 90, 91 92 are varied to change the character height over a range of more than 2:1 while maintaining sharp focus. The lens .thus functions like a zoom lens of the optical art.

Another improvement over the embodiment of FIG- URE 3 is the addition of ferromagnetic pole pieces 93, 94 inside the tube envelope. Pole pieces 93, 94 are washershaped discs of soft iron, ferrite, or other magnetic material, and are located directly inside the pole pieces of the external coil 89. Internal pole pieces improve the eliciency of the rotation coil and thus reduce the power required to achieve la given rotation. F-urthermore, the internal pole pieces reduce the leakage of magnetic flux from the rotation coil and thus make the character size controls, rotation controls, and deection controls more perfectly independent.

It will be obvious to one skilled in the art that variations described under FIGURE 3 are also applicable to FIGURE 4. The combination of various features of the FIGURE 3 embodiment and the FIGURE 4 embodiment are also obvious, e.g., a rotation coil without internal pole pieces may be used with an electrostatic size control lens. Furthermore, it will be obvious that the entire coil could be placed inside the crt envelope and that the size control lens could be a non-rotational magnetic lens, in which two coils and two air gaps producing opposing axial ux are used. In this variation, the non-rotational lens could be used only for size control, with a separate rotation coil used to control orientation, or the two coils of the double gap lens could be used for both size and orientation control by unbalancing the currents in the two windings.

In the further embodiment of FIGURE 5, the novel feature of electrically controllable character rotation is added to a shaped beam tube of the magnetic convergence type. The electron gun 5, rotation coil 89, and deflection coils 23 operate similarly to the corresponding elements of FIGURE 3. Conventional selection and reference plates are shown to illustrate this embodiment but obviously coplanar plates could be used to improve the quality and precision of the display. The electron gun shown (except for the rotation coil 89) is representative of the model C7C Charactron Shaped Beam Tubes. The electron beam is deflected off axis 6 by conventional electrostatic plates 80, 81 so as to strike one of the many character shaped apertures in the mask 9. Before striking the mask the beam enters the field of the magnetic convergence coil 96, a coil of long solenoidal form having a substantially uniform axial field. The beam is twisted into a spiralling path by the magnetic field of coil 96 and strikes the mask 9 at a point which is rotated 45 about the tube axis with respect to the original plane of deflection produced by plates 80, 81. After passing through the mask the beam has a cross section in the shape of the desired character. The central electron of the shaped beam continues to spiral about the tube axis as the beam proceeds through the field of coil 96, and simultaneously the noncentral electrons of the beam rotate about the central electrons path. The direction of the central electron as it laves the field of coil 96 is such that it would intersect the tube axis in the region of reference plates 86, 87. If the initial deflection were vertical, produced by plates 81, then the desired axis crossover is in the center of plates 87. The beam entering plates 86 is nearly on axis but not traveling parallel to the axis; the electrostatic field of plates 87 bends the beam to a path parallel to (and on) the axis. Note that the beam was given an initial vertical component of velocity by plate 81; reference or compensation to return the beam to a paraxial velocity is achieved with a horizontally oriented field in plates 87, because of the spiralling of the path of the central electron within the coil 96. The shaped beams cross section also is rotated about the central electrons path 45 by the latter half of the field of coil 96. In FIGURE 5, the control of character orientation by coil 89 is achieved in a manner identical to FIGURE 3. In each case, rotation is achieved after the characters are referenced back on and parallel to the axis.

In the embodiment of FIGURE `6 the magnetic convergence coil and the rotation coil are combined into a single coil 98 which also focuses the beam. The path of the beam in the tube from the electron gun to the detiection coils 23 is the same as in FIGURE 5. When it is desired to change the -orientation of the displayed characters, the rotation control circuits 99 reverse the direction of curent in the coil 98 as supplied from convergence current control circuits 100. Simultaneously, the rotation control 99 interchanges the horizontal and vertical signals derived from the character selection control circuits 11 and passed to character selection plates 80, 81 and interchanges also the horizontal and vertical reference signals from reference control circuits 102 to reference plates 86, 87. The interchange of horizontal with vertical selection signals is necessary because the beams spiralling prior to striking the mask 9 is now to a point 45 in a direction opposite the original spiralling. The reference signals are also interchanged to maintain the continued requirement that selection and reference be oriented at to each other. The cross section of the character-shaped beam leaving plates 87 will thus rotate 90 degrees whenever the rotation control 99 is reversed, and characters of both orientations will remain in sharp focus.

The rotation control circuits 99 are shown on FIGURE 6 as three double-pole, double-throw switches, each connected as a reversing switch, and all Iganged together. rIhe rotation control can obviously be implemented by relays or preferably by semiconductor switching circuits to perform the same function. The convergence current control circuits 100 with the accompanying switch which reverses the current in the coil 98 are in essence similar to the circuit of FIGURE 2.

In all of the embodiments described herein, workable variations may be made in which the rotation exceeds 45 degrees; in fact, a rotation of any odd integral multiple of 45 degrees is generally workable (l 45, 3 45, SX45, etc.). Furthermore, applications in which the desired change in orientation of the displayed characters is other than 90 degrees are possible; e.g., if a change of 180 degrees is desired, the rotation coil is adjusted to produce plus/minus 90 degrees rotation.

It is evident therefore that this invention provides an improved and ypractical manner of changing at will the orientation of characters shaped by an apertured mask or other means such as emission or deflection controls operable upon the beam to form a shaped beam, wherein the orientation of the shaped beam may be simply programmed by electronic controls in a display system. Those novel features of this invention believed to be representative of the spirit and scope of the contribution to the advancement of the art are therefore defined with particularity in the appended claims.

What is claimed is:

1. The method of inclining characters formed from a shaped electron beam on the face of a cathode ray tube comprising the step of rotating the shaped electron beam about its axis selectively in opposite directions.

2. Means for selecting character inclination in displays on a cathode ray tube comprising in combination, an electron gun, means for shaping an electron beam from said gun to display a predetermined pattern shape, electromagnetic means operable upon said shaped beam for rotating the pattern in response to electric current fiow, and means selectively reversing current ow through said electromagnetic means to establish different inclinations of said pattern upon said screen.

3. Means as defined in claim 2 wherein the electromagnetic means operable upon the shaped beam both focuses and rotates the pattern.

4. Means as defined in claim 3 wherein the electromagnetic means is at least two coils substantially coaxial with said shaped beam and disposed at different places along the path of the beam, at least one of said coils being adjusted to produce clockwise rotation of said beam and at least one other of said coils being adjusted to produce counter-clockwise rotation, such that a net rotation of the beam is effected.

5. Means as defined in claim 4 wherein current levels are established in said coils to cause a net beam rotation of an integral multiple of 45 degrees.

6. Means as defined in claim 4 wherein one of said coils is a convergence coil, and the means for shaping the beam is an aperture mask disposed in the path of the beam and located at an intermediate position within said convergence coil.

7. Means as defined in claim 3 wherein the electromagnetic means consists of a single coil extending along the beam path and operable to control convergence of the beam.

8. Means as defined in claim 7 wherein the means for shaping the beam is an aperture mask disposed in the path of the beam and located at an intermediate position within said single coil.

9. Means as defined in claim 2 wherein a current level is established through said electromagnetic means to cause a beam rotation of an integral multiple of 45 degrees.

10. Means as defined in claim 2 wherein the means selectively reversing current ow comprises a two channel transistor switching circuit repsonsive to a change in input waveform level to select one of said channels, wherein each channel delivers current to said electromagnetic means in opposite directions.

11. Means as defined in claim 2 wherein the electromagnetic means is an electromagnet having a component of magnetic flux parallel to the path of said electron beam.

12. Means as defined in claim 2 wherein the electromagnetic means is a coil of conductive material substantially coaxial with said electron beam.

13. Means as defined in claim 2 wherein the means for shaping the electron beam is an apertured mask disposed in the path of the beam.

14. Means as defined in claim 2 including means operable on said beam for changing character size.

15. Means as defined in claim 2 wherein the tube includes electrostatic convergence lens means.

References Cited UNITED STATES PATENTS 2,761,988 9/1956 McNaney.

RODNEY D. BENNETT, Primary Examiner.

C. L. WHITHAM, Assistant Examiner.

U.S. Cl. X.R. 

